1. Field of the Invention
The present invention generally relates to a transformer.
2. Description of Related Art
In a balanced-unbalanced band pass filter, an interactive magnetic coupling between two inductors constituting the transformer is used to generate a mutual induction, so as to deliver a differential signal on a single end. Under the miniaturization trend of electronic products, electronic components are integrated in a circuit substrate, for example, capacitors, inductors, resistors, and other passive components. In the transformer, two inductors formed by a coil may be achieved through a circuit layout of the circuit substrate.
FIG. 1 shows a conventional transformer. Referring to FIG. 1, the conventional typical transformer includes a first inductor L1 and a second inductor L2. Through an interactive electromagnetic induction between the first inductor L1 and the second inductor L2, an input voltage between two ends of the first inductor L1 is converted into an output voltage between two ends of the second inductor L2. Theoretically, a ratio of the input voltage to the output voltage is equal to a ratio of the first inductor L1 value to the second inductor L2.
FIG. 2 shows another conventional transformer. Referring to FIG. 2, different from the typical transformer of FIG. 1, the transformer of FIG. 2 may convert a single signal into a differential signal pair. The transformer of FIG. 2 includes a first capacitor C11, a first inductor L11, a second capacitor C12, a second inductor L12, a third capacitor C13, and a third inductor L13. A first mutual inductor Lm11 is generated by an interaction between the first inductor L11 and the second inductor L12, and a second mutual inductor Lm12 is generated by an interaction between the first inductor L11 and the third inductor L13. Through the first mutual inductor Lm11 and the second mutual inductor Lm12, a signal input to a first port P11 is converted into a differential signal pair, and then output through a second port P12 and a third port P13.